This invention relates generally to electrically controlled unit injectors, and more specifically to unit injectors having a timing function and metering function, both of which are controlled by a single solenoid, three-way valve unit.
Considerable development work is being done in the area of electrically controlled unit injectors, particularly to increase the precision with which the timing and metering functions are performed. The results of a portion of such development work are described in the above referenced patent issued to Messrs. Sisson and Lewis. In the Sisson-Lewis development, the metering phase of operation is terminated by opening a control valve and increasing the pressure in the timing chamber, thereby causing the metering plunger to stop when sufficient pressure is developed in the timing chamber. This system of terminating metering depends somewhat on the fluid dynamics of the fuel supply to the timing chamber and the dynamics of the metering plunger. While these dynamics can be readily accommodated, it has been found that cutting off the fuel supply to the metering chamber creates precise control of the amount of fuel in the metering chamber without significant regard for the above noted dynamics.
Also, an aspect of the fluid dynamics is the desirability of a large area passageway to the timing chamber, thus ensuring rapid pressurization of the timing chamber to quickly stop the travel of the metering plunger. In this situation, if the passageway is significantly long, the fuel in the passageway must be compressed, along with the fuel in the timing chamber, during injection. This additional fuel to be compressed places additional requirements on the cam profile to increase the speed of the pumping plunger at the start of injection.
In certain other designs, the fuel being supplied to the metering chamber is pressure regulated to effectively control the metering process. The elements associated with this regulator can add to the cost of the injector and provide additional design considerations.
As a general consideration, unit injectors of the type disclosed herein are well known. Consider for example the injector and system disclosed in the above referenced Sisson-Lewis patent and the art cited in connection with the filing and prosecution of that application.
In the Sisson-Lewis disclosure, a unit injector of the same general type as the unit injector of the instant invention is disclosed. In that disclosure, a fuel injector (10) is provided for each cylinder of an internal combustion engine, the injector including an electronically operated control valve (146) disposed between supply passage (42) and a timing chamber (98) to control the admission of fuel into and out of the timing chamber. A primary pumping plunger (62) and a secondary plunger (90) are axially spaced within the central bore of the injection body, and a normally closed injection nozzle (14) is situated at one end of the injector body. A mechanical linkage (27,28,30) associated with the camshaft of the engine drives the primary pumping plunger (62) against the bias of a main spring (18). The timing chamber (98) is defined between the plungers (62, 90) and a metering chamber (128) is defined between the secondary plunger (90) and the nozzle (14).
An electronic control unit (52) responds to engine operating conditions, and delivers a signal to the control valve (146) to close the valve and seal the timing chamber for a controlled period of time. The sealed timing chamber forms a hydraulic link, so that the plungers (62,90) move in concert during the injection and metering phases of the cycle of operation. When the signal from the ECU is terminated, the control valve opens, and breaks the hydraulic link so that the primary plunger (62) moves independently of the secondary plunger (90) which is biased in a set position by a spring (96) after termination of the control signal.
The timing function can be adjusted by the ECU relative to any preselected position of the crankshaft to optimize engine performance, while the metering function is achieved in a proportionate manner relative to the degree of camshaft rotation. A cam (22), having a linear portion, controls the mechanical linkage, and thus the primary pumping plunger (62), to produce the proportional metering function.
U.S. Pat. No. 3,951,117, granted Apr. 20, 1976 to Julius Perr, discloses a fuel supply system including hydraulic means for automatically adjusting the timing of fuel injection to optimize engine performance. The embodiment of the system shown in FIGS. 1-4 comprises an injection pump 17 including a body 151 having a charge chamber 153 and a timing chamber 154 formed therein. The charge chamber is connected to receive fuel from a first variable pressure fuel supply (such as valve 42, passage 44, and line 182), and the timing chamber is connected to receive fuel from a second variable pressure fuel supply over line 231, while being influenced by pressure modifying devices 222 and 223. The body further includes a passage 191 that leads through a distributor 187 which delivers the fuel sequentially to each injector 15 within a set of injectors.
A timing piston 156 is reciprocally mounted in the body of the injection pump in Perr between the charge and timing chambers, and a plunger 163 is reciprocally mounted in the body for exerting pressure on the fuel in the timing chamber. The fuel in the timing chamber forms a hydraulic link between the plunger and the timing piston, and the length of the link may be varied by controlling the quantity of fuel metered into the timing chamber. The quantity of fuel is a function of the pressure of the fuel supplied thereto, the pressure, in turn, being responsive to certain engine operating parameters, such as speed and load. Movement of the plunger 163 in an injection stroke results in movement of the hydraulic link and the timing piston, thereby forcing fuel into selected combustion chamber. The fuel in the timing chamber is spilled, or vented, at the end of each injection stroke into spill port 177 and spill passage 176. The mechanically driven fuel injector, per se, is shown in FIGS. 14-17.